A neuron has two types of neurites, i.e., a dendrite that accepts information from another neuron and an axon that sends out information to another neuron. The extinction of neurons or the atrophy of neurites due to various causes inhibits a normal information transfer between neurons, so that various diseases are caused depending on the region of the nervous system that has been damage. Specific examples of the diseases caused by damage of the central nervous system (brain, spinal cord) include Parkinson's disease, Alzheimer's disease, and amyotrophic lateral sclerosis and specific examples of the diseases caused by damage of peripheral nerves include polyneuropathy and Guillain-Barré syndrome. Particularly, the disease of the central nervous system is progressive, and an effective treatment technique for the disease has not been developed yet. Although a neurotrophic factor-like agonist is studied as a therapeutic agent for the disease of the central nervous system, such an agonist has mainly neuroprotective effect and the neurite-outgrowing activity of the agonist under neurodegenerative circumstances has not been clearly shown. As the treatment for the neurodegenerative disease, it is necessary not only to inhibit the death of a neuron, but also to outgrow a neurite of a residual neuron to normalize the information transfer between neurons, so that the development of a therapeutic agent for a neurodegenerative disease that has both a neuron death-inhibiting activity and a neurite-outgrowing activity is desired.
On the other hand, it is known that sominone, which is a compound extracted from Indian ginseng, has an excellent neurite-outgrowing activity (Patent Document 1) and that withanoside IV has an outgrowing activity of an axon of a spinal cord cell (Patent Document 2).